The parse_config_key() function was introduced to make it
easier to match "section.subsection.key" variables. It also
handles the simpler "section.key", and the caller is
responsible for distinguishing the two from its
out-parameters.
Most callers who _only_ want "section.key" would just use a
strcmp(var, "section.key"), since there is no parsing
required. However, they may still use parse_config_key() if
their "section" variable isn't a constant (an example of
this is in parse_hide_refs_config).
Using the parse_config_key is a bit clunky, though:
const char *subsection;
int subsection_len;
const char *key;